Arrange the following compounds in increasing order of their acidic strength :
Propan -1-ol 2, 4, 6-trinitrophenol, 3-nitrophenol, 3, 5-dinitrophenol, phenol, 4-methylphenol.

Explanation

To arrange the compounds in increasing order of their acidic strength, we need to analyze the structures and the effects of substituents on acidity. Here's a step-by-step breakdown of the solution:

### Step 1: Identify the Compounds
The compounds given are:
1. Propan-1-ol
2. 2,4,6-trinitrophenol
3. 3-nitrophenol
4. 3,5-dinitrophenol
...